[Paper Review] Subroutines to Simulate Fission Neutrons for Monte Carlo Transport Codes

J. P. Lestone|arXiv (Cornell University)|Sep 17, 2014

Nuclear Physics and Applications1 references4 citations

TL;DR

This paper presents Fortran subroutines—getnv252, getnv240, getnv239, and getnv235—that simulate fission neutrons from 252Cf, 240Pu, 239Pu, and 235U, accurately reproducing neutron multiplicity moments and neutron-neutron correlation data. The subroutines enable advanced applications in neutron coincidence imaging and transparency measurements by modeling realistic fission neutron emission characteristics.

ABSTRACT

Fortran subroutines have been written to simulate the production of fission neutrons from the spontaneous fission of 252Cf and 240Pu, and from the thermal neutron induced fission of 239Pu and 235U. The names of these four subroutines are getnv252, getnv240, getnv239, and getnv235, respectively. These subroutines reproduce measured first, second, and third moments of the neutron multiplicity distributions, measured neutron-fission correlation data for the spontaneous fission of 252Cf, and measured neutron-neutron correlation data for both the spontaneous fission of 252Cf and the thermal neutron induced fission of 235U. The codes presented here can be used to study the possible uses of neutron-neutron correlations in the area of transparency measurements and the uses of neutron-neutron correlations in coincidence neutron imaging.

Motivation & Objective

• To develop accurate, reusable Fortran subroutines for simulating fission neutron emission in Monte Carlo transport codes.
• To reproduce measured first, second, and third moments of neutron multiplicity distributions for key fissile isotopes.
• To model neutron-fission and neutron-neutron correlation data for both spontaneous and thermal neutron-induced fission.
• To support advanced applications such as coincidence neutron imaging and transparency measurements using neutron-neutron correlations.
• To make previously published, specialized simulation tools more accessible to a broader research community.

Proposed method

• The subroutines are implemented in Fortran and designed for integration into existing Monte Carlo transport codes.
• They use empirical data on neutron multiplicity distributions to simulate the number of neutrons emitted per fission event.
• Neutron-fission and neutron-neutron correlation data are incorporated to model angular and energy correlations between emitted neutrons.
• The simulation of 252Cf spontaneous fission includes measured first, second, and third moments of multiplicity and neutron-fission correlations.
• For 235U and 239Pu, thermal neutron-induced fission is modeled using measured neutron-neutron correlation data.
• The subroutines are based on a 1999 Los Alamos National Laboratory report (LA-UR-99-5444), updated for wider dissemination.

Experimental results

Research questions

• RQ1 How can fission neutron emission be accurately simulated in Monte Carlo transport codes using empirical data?
• RQ2 To what extent can neutron multiplicity moments and neutron-neutron correlations be reproduced in simulation?
• RQ3 Can these subroutines enable new applications such as coincidence neutron imaging or transparency measurements?
• RQ4 How do the simulated correlations compare to measured data for 252Cf and 235U fission?
• RQ5 What is the impact of making these specialized simulation tools publicly available to the research community?

Key findings

• The subroutines successfully reproduce measured first, second, and third moments of neutron multiplicity distributions for 252Cf, 240Pu, 239Pu, and 235U fission.
• Neutron-fission correlation data for spontaneous fission of 252Cf are accurately modeled by the getnv252 subroutine.
• Neutron-neutron correlation data for both 252Cf spontaneous fission and 235U thermal neutron-induced fission are well-reproduced by the respective subroutines.
• The simulation framework enables realistic modeling of neutron emission for applications in coincidence imaging and transparency measurements.
• The subroutines are validated against experimental data and are suitable for integration into Monte Carlo transport codes.
• The codebase is publicly released to support broader research in neutron-based detection and imaging techniques.